Codelearn Playground now has Rails 4.
Recently Nitrous.io made a lot of wave by providing free Rails 4 online IDE on the browser. I decided to extend Rails 4 support on Codelearn Playground, which is also like an online Rails IDE augmenting Codelearn Rails Tutorials.
You would need to sign up on Codelearn to use the IDE. Also, the Codelearn tutorial is based on Rails 3. I deployed a nice hack to expose both Rails 3 & 4 on Codelearn Playground which I have documented in this blog post